This invention relates generally to gas heaters comprising fireplaces having fireboxes, and more specifically to fireboxes for direct vent and vent-free gas fireplaces. The invention may also be used without gas burners and instead with conventional wood burning fireplaces such as fireplace inserts which are typically added after a home is built.
The many advantages of fireplaces have been known for centuries. Today, fireplaces are desired and used chiefly for decorative purposes or as supplemental heating sources for homes. Not only can they provide a reliable, cost effective source of heat, but they are always considered to add a soothing, entertaining, and attractive atmosphere to a home.
It is no surprise then that fireplaces are becoming increasingly popular. Recent developments in gas fired fireplaces have resulted in versatile fireplace units that in some cases are freestanding and that in other cases may be installed relatively easily and inexpensively as compared to their woodburning counterparts that quite often require extensive construction and design considerations to install, especially after the home is first built. Modern fireplaces, however, are not without application difficulties that may interfere with their use and enjoyment. For instance, in many cases fires may only be tolerated for shortened time periods because of the intense heat that they can produce. This problem is especially evident when entertaining groups of people in a room with a fireplace. The temperature in the room quickly becomes unacceptably warm, leaving the host of the gathering with the choice of turning off the fireplace or opening windows. Neither of these options is desirable. Opening windows will create chilly drafts and noticeably warm and cool spots in the room, while shutting down the fireplace will detract from the ambiance of the room. Too often, the aesthetics of the fireplace are sacrificed because the room becomes too hot, too soon. Indeed, many gas-fired fireplaces are equipped with sensors that will shut the fire down when either the temperature of the fireplace or of the room reaches a predetermined set point, all to the dismay of the fireplace owner when the fireplace shuts down in a matter of minutes once a gathering begins.
Although as expected the firebox itself becomes very hot as a fire burns within it, the top area of the combustion chamber becomes especially hot as the heat naturally rises and concentrates at the horizontal beam spanning the top front of the firebox opening. This concentrated heat, if not properly insulated, literally bakes the surrounding building materials, such as wood studs and the finish materials as well. This not only shortens the life and sacrifices the appearance of the finish, but also is an ineffective use of the heat. Furthermore, as these surrounding building materials heat up, they themselves become a source of radiant heat which further intensifies the heat emanating into the room from the fireplace.
Finally, the warmth from a fireplace and the use of room air for combustion increases the negative pressure of a home in relation to the outside atmosphere. Thus, when an outside door is opened, it can cause a rush of cold heavy air into the home. The blast of cold air is always unwelcome and a warm fire only intensifies this experience. To alleviate these undesirable effects, quite often a homeowner will crack open a window while a fire is burning in a fireplace. Unfortunately, this often creates a chilly draft which is also undesirable.
One solution offered by several prior art devices is to provide outside air to the fireplace, not just for combustion purposes, but to more efficiently harness the heat of the fireplace by circulating cold outside air around the firebox to simultaneously heat the outside air and cool the firebox, thereby more efficiently using the heat generated by a fire while concurrently introducing cooler air into the room and alleviating the intense heat emanating from the fireplace. One such example is found in U.S. Pat. No. 4,928,667 which incorporates a blower to force outside air through a heat exchanger having a serpentine path and then into the room. While this arrangement does serve to capture heat which might otherwise escape through the flue, it requires a blower to force the outside air through the heat exchanger and yet does not reduce the heat concentrated at top of the firebox opening. Furthermore, the addition of a blower increases the initial cost and complexity of the fire place, and also the energy cost and maintenance over its useful life.
Fireplaces having fireboxes of prior art design are therefore disadvantaged in that they either suffer from intense heat generation which can force them to be shut down or otherwise inefficiently mix in outside air at increased cost and without eliminating the concentration of heat at its most intense point of build up, they can inefficiently transfer heat to building materials surrounding this point of concentrated intense heat, and they can increase the negative pressure in the home relative to the outside atmosphere.